The concept of bio-fuel may be on the brink of a global resurrection, as sequential cropping may provide feed-stock for bio-fuel production without impacting food production, according to research by Ecofys.

While bio-fuels have become increasingly unpopular, farmers face other problems when it comes to cultivation – the loss of soil quality due to mono-crop farming practices. Mono-cropping itself comes with considerable negative externalities, including, among others, lower soil quality; soil erosion; increased dependence on synthetic fertilisers, that are themselves carbon intensive to produce; as well as decreased carbon uptake into soil.

In a new analysis from Ecofys, titled ‘Assessing the case for sequential cropping to produce low ILUC risk bio-methane’, the consultancy firm explored the potential of killing two birds with one stone, as well as the wider impact of such a move on negative externalities.

The publication found that sequential cropping has other benefits, including improved soil quality; increased regional biodiversity; decreased need for synthetic fertilisers; and improved farming productivity. The business case for the practice was found to be significant as well.

In recent years, the negative knock-on consequences of bio-fuel cultivation have led to it no longer being seen as one of the solutions to addressing the planet's greenhouse gas (GHG) excess. However, the 2016 ratification of the Paris Agreement pushing nations to limit emissions to limit the planet's warming to beneath 2C, including the considerable burden agriculture produces on global GHG emissions – around a 12% of global greenhouse gas emissions coming from agriculture – mean that bio-fuels may still be central to transforming agricultural waste.

Support for the bio-fuels industry previously crumbled due to its negative impact on a range of fronts, from its indirect land use changes resulting in a ‘food versus fuel’ dilemma, to wider impacts on biodiversity and carbon stocks – as high bio-diversity areas and carbon sinks including forested areas were controversially clear cut for bio-fuel cultivation, as the market oversaw a completely irrational implementation of a supposedly greener fuel economy. Within the EU, this has resulted in growing calls to halt crop-based bio-fuels, coupled with increased focus on non-land-based bio-fuels from animal waste and residue materials.

The focus of the study falls largely on whether sequential cropping, or crop rotations (at a case study farm) allow for the sustainable production of bio-fuels. The study, which is based on research at the Palazzetto farm Italy, looks at the wider implications of sequential cropping on generating material for bio-fuels, how it affects the land, water use as well as the business case for the practice.

Palazetto Farm

Palazzetto is a large farm with 255 hectares of land and a stable of 650 cows, 300 of which produce milk, along with a bio-gas installation with a production capacity of 1MW of electricity. Since 2011 the farm has introduced sequential cropping, prior to which the farm produced the singular feed of maize, in a mono-crop structure where the plant was grown in the summer before a ‘fallow’ period in which the land lay bare.

The new crop rotation scenario saw the land being used to grow triticale straw instead during the former fallow period, enabling the land to produce silage material for the bio-gas plant's anaerobic digestion system – as well as further feed for livestock. Double-cropping in this instance led to the land increasing in productivity on both fronts, rather than food production being substituted for that of bio-fuel.

The result of the sequential cropping on forage unit production stood at 17,864 in maize silage for the mono-crop, while sequential cropping saw the land produce 11,804 in triticale silage and 16,355 in maize silage for 28,159 in total silage.

While the land was able to produce considerably more silage for use in the wider bio-fuels value chain, the negative externalities of the production may outweigh the benefits. To better understand the consequences, Ecofys considered the effect of increased productivity on the land, water and business case for the case study farm.

In this regard, the value of additional crops per year has, for millennia, been understood as beneficial to soil quality; nitrogen fixers, such as legumes, are able to do the work of synthetic fertilisers, while a diverse range of plants is able to benefit not merely soil heath but wider biodiversity across a region, including plots of flowers for bees and other pollinators, and seeds for birds.

However, further to this, the research by the renewable energy consultancy found that sequential crops saw increased soil carbon uptake, from 2.5% to 3% on two out of three pilot fields. The increase in soil organic carbon at Palazzetto was, the firm noted, “very good for the overall soil quality.” In addition, soil nutrient levels were found to have increased exponentially, nearly eradicating the farm’s need to use synthetic fertilisers, by applying bio-gas digestate manure instead. The results also demonstrated a clear improvement in soil bio-diversity, as the earth began providing a range of micro-nutrients to plants in the area.

In terms of GHG emission, comparing the gCO2 eq/MJ of bio-methane to fossil fuels, the co-digestion of manure with both crops has huge potential to reduce emissions from bio-methane production, compared to maize-manure alone.

The business case for running a sequential crop at the case study farm also makes for compelling reading, with Ecofys finding that the total cost of running maize silage & triticale silage during sequential cropping was not significantly higher in Euros per hectare than a maize silage mono-crop, with considerable synergies between the crop cycles cutting total costs. The reduction in maize output in sequential cropping was also found to be minor in relation to the mono-crop method.

Alongside this minimal negative impact, according to the consulting firm's analysis, the benefits of dual-production are relatively robust, with the paper's authors stating, “We note a 21% decrease in feed costs and a 42% decrease in bio-gas feedstock costs. This will be the most important reason for farmers to invest in sequential cropping as a yield increase measure.”

Introducing maize and triticale sequential cropping without displacing other crops would be replicable across areas in Italy and France totalling at least 1 million of hectares. However, the report also notes that while the case at Palazzetto produces promising results, more study into potential negative effects of the practice (in different climates, water conditions, etc) is needed, while drawing up safeguards to protect bio-diversity from inefficient, unnecessary, and irreversible, incursion is also essential.